The present invention relates to fuel burners and methods for combusting solid fuels with oxidants, including but not limited to oxygen and oxygen-enriched air, and in particular to such burners and methods for combusting pulverized solid fuels for generating heat in industrial melting furnaces for glass, ceramic materials, metals, etc.
However, the invention is not limited to use with such industrial melting furnaces. Persons skilled in the art will recognize that the burners and methods of the present invention may be used in many other fired process heating applications, including but not limited to cement kilns and steam generators.
Solid fuel burners and methods for combusting solid fuels with oxidants, such as oxygen and/or oxygen-enriched air, are well known. Various types of such burners have been developed for different industries (e.g., glass melting), including oxy-fuel burners having concentric or coaxial passages for supply of fuel and oxygen. Such burners are disclosed in U.S. Pat. No. 5,104,310 (Saltin); U.S. Pat. No. 5,743,723 (Iatrides, et al.); and U.S. Pat. No. 6,685,461 (Rio, et al.). Other such burners are taught in U.S. Pat. No. 3,894,834 (Estes); U.S. Pat. No. 4,797,087 (Gitman); U.S. Pat. No. 4,902,223 (Young); U.S. Pat. No. 4,928,605 (Suwa, et al.); U.S. Pat. No. 6,843,185 (Taylor); and U.S. Patent Application Publication No. 2003/0075843 (Wunsche).
For example, U.S. Pat. No. 3,894,834 (Estes) discloses an axially positioned oxy-fuel burner within a coal/air burner for adjusting flame length and maintaining stability.
U.S. Pat. No. 5,743,723 (Iatrides, et al.) discloses a three-tube oxy-fuel burner comprising: an oxidant source of at least 80% oxygen; an outer and an inner oxidant passage, each connected to the oxidant source; a fuel conducting passage disposed between the two oxidant passages; and a valve to regulate the flow between the oxidant passages.
U.S. Pat. No. 6,685,461 (Rio, et al.) discloses a burner similar to that of Iatrides, et al. in the '723 patent, but with several structural and operational differences. For example, the burner is fastened to a burner quarl, and a control valve is housed in the burner for adjusting oxidant flows between the two oxidizer tubes. No limits are specified for the oxygen concentration of the oxidant.
U.S. Pat. No. 5,104,310 (Saltin) discloses an oxy-fuel burner with several configurations, each requiring a central oxygen nozzle connected to an oxygen-receiving chamber (which is part of the burner), at least one fuel nozzle radially spaced from the central oxygen nozzle, and at least one peripheral oxygen nozzle at a greater radial distance from the central oxygen nozzle (relative to the fuel nozzle(s)). Several variations include one or more of the following features: part of the means for supplying fuel and oxygen to the burner is a cooling jacket for the burner; peripheral oxygen nozzle(s) of a converging-diverging design; and a fuel nozzle that transmits only fuel (i.e., no carrier gas).
In addition to the oxy-fuel burners discussed above, many other solid fuel burners have been developed for burning pulverized coal and other fuels. Such burners are disclosed in U.S. Pat. No. 4,497,263 (Vatsky, et al.); U.S. Pat. No. 5,090,339 (Okiura, et al.); U.S. Pat. No. 6,715,432 (Tsumura, et al.); U.S. Pat. No. 6,752,620 (Heier, et al.); U.S. Pat. No. 6,889,619 (Okazaki, et al.); and JP 60-194208 (Takayuki Abe).
In addition, various devices have been developed for use with pulverized coal-fired burners and furnaces, especially during low load operations. For example, U.S. Pat. No. 4,274,343 (Kokkinos) discloses a device for stabilizing ignition of coal-fired flames during low load operation. U.S. Pat. No. 4,448,135 (Dougan, et al.) and U.S. Pat. No. 6,475,267 (Lehn) disclose different types of such devices for use with burners.
The burners and devices discussed above have addressed various problems relating to fuel burners and methods for combusting solid fuels. However, many problems remain, or have not been satisfactorily addressed.
For example, the prior art has not taught a burner and method for combusting a solid fuel which satisfactorily and simultaneously attain robust flame stability, enhanced turndown, adjustability of flame properties, and the ability to combust solid fuels of greatly varying properties, in particular, both high and low volatile solid fuels (including petroleum coke).
Other problems that occur with conventional solid fuel burners, especially at turndown (i.e., reduced firing rate) conditions, include weakening of the axial momentum of the burner flame, the loss of coherent flame structure, and shortening of the flame. In general, the prior art burners do not maintain a constant (or nearly constant) flame length over an entire operating regime.
There are fuels and/or combustion applications for which oxygen/fuel (so-called oxy/fuel) combustion or oxygen-enriched air/fuel combustion provide superior results relative to air/fuel combustion. While there are prior art patents pertaining to oxygen-based, solid fuel combustion [(e.g., U.S. Pat. No. 4,928,605 (Suwa, et al.) and U.S. Pat. No. 4,902,223 (Young)], these patents do not satisfactorily and comprehensively address the aforementioned problems while also attending to the challenges distinctive to oxygen-based combustion. Such challenges relate primarily, but not exclusively, to the high temperature created by oxygen-enhanced flames and the potentially detrimental effect that these flames can have on burner and furnace components. Buffering of the burner components from the high temperature oxygen-enhanced flame is often accomplished by the use of water-cooled jackets. Although such jackets nominally protect the burner components from many instances of high temperature damage, the jackets add complexity and cost to the operation, while not mitigating against one of the principal causes of high temperature damage, which is control of flow distribution (i.e., flow profiles within the burner nozzle) and mixing patterns of the reactants. In the case of solid fuel combustion, inadequate control of reactant flow distribution and mixing leads not only to high temperature damage, but also to impingment of solid particles and subsequent erosion of burner and furnace components.
In view of these and many other problems pertaining to prior art burners and methods for combustion of solid fuels with oxidants, it is desired to have a burner and a method for combustion which overcome the difficulties, problems, limitations, disadvantages, and deficiencies of the prior art to provide better and more advantageous results.
It is further desired to have a more efficient burner and method of combustion for combusting a solid fuel with an oxidant.
It is still further desired to have a burner and a method for combusting a solid fuel which attain robust flame stability, enhanced turndown, adjustability of flame properties, and the ability to combust solid fuels of greatly varying properties, in particular both high and low volatile solid fuels.
It is still further desired to have a burner and a method for combusting a solid fuel which achieve a longer, slower mixing flame with lower peak temperature than would otherwise be achieved with prior art burners and methods.
It is still further desired to have a burner and a method for combusting a solid fuel which efficiently operate over a wider range of firing rates than is normally attainable with burners and methods of the prior art.
It is still further desired to have a burner and a method for combusting a solid fuel which strengthen the axial momentum of the burner flame and prevent the loss of coherent flame structure that occurs with conventional solid fuel burners and combustion methods.
It is still further desired to have a burner and method for combusting a solid fuel which facilitate lengthening of the burner flame at reduced loads, and thereby provide a means for maintaining nearly constant flame length over an entire operating regime.
It is still further desired to have a burner and a method for combusting a solid fuel capable of stably burning low volatile solid fuels, such as petroleum coke.
It is still further desired to have a burner and a method for combusting a solid fuel wherein flame properties can be adjusted via control of reactant mixing properties.
It is also desired to have a burner and method for combusting a solid fuel capable of supporting oxygen-enhanced or oxygen-fuel combustion.